Recently, there have been various reports on the benefit which tryptophan is believed to have on several aspects of human behaviour, mood, brain function, brain development, when such tryptophan is taken up by the brain. Examples of such reports are WO 99/55174, WO 00/42868, WO 2005/023017.
Tryptophan is an amino acid present in many proteins, like e.g. whey proteins, but also animal protein contains tryptophan. Tryptophan can be taken up in the blood, and from the blood into the brain, after ingestion of a protein which contains tryptophan. However, tryptophan is not the only amino acid taken up, and in fact when an average animal protein composition is ingested, the level of tryptophan taken up by the brain is so low due to competitive uptake of other amino acids that usually no significant effect can be observed attributable to tryptophan. Hence, most of the reports referred to above either use proteins or protein-fractions rich in tryptophan, or the free amino acid tryptophan (the latter optionally in combination with other free amino acids and/or proteins).
Use of tryptophan as free amino acids has disadvantages, in that food legislation in many countries limits the use of tryptophan as free amino acid in foodstuffs. Tryptophan-rich proteins have natural limits to the level of tryptophan and its ratio to large neutral amino acids, which is relevant for uptake of tryptophan by the brain.
Recent insight is that peptides rich in tryptophan can be a good source to get sufficient tryptophan in the brain for the desired effects and may be easier applied in foodstuffs than free amino acids. Such peptides rich in tryptophan are preferably low in amino acids with which competition in uptake into the brain is believed to be high: the so-called large neutral amino acids (LNAA), which are: leucine, isoleucine, valine, tyrosine, phenylalanine (and depending on the definition of LNAA one uses also methionine). Hence, it is preferred to make and use peptide preparations which contain a high level of tryptophan and have a high ratio tryptophan/LNAA. Methionine is considered not to have any beneficial metabolic effect in the context of this invention, and is thus for the purpose of this invention not considered as one of the LNAA.
WO 02/46210 describes a method for preparing tryptophan-rich peptides with a ratio tryptophan/LNAA of at least 0.3 on weight basis, by hydrolysis of e.g. alpha-lactalbumin and selective precipitation.
Tryptophan-rich peptide preparations such as e.g. described above can be used in foodstuffs. Such foodstuffs can be dry, like a snack bar, or breakfast cereals, or a powder which can be dispersed/dissolved in a liquid like water or milk to obtain a drinkable product.
There is also a desire to manufacture liquid products containing tryptophan-sources (and preferably a tryptophan-source which is/are a tryptophan-rich peptide fractions, and preferably having a beneficial tryptophan/LNAA ratio) which are e.g. ready to drink (RTD) products as there is an increasing tendency in e.g. Europe to provide functional foods in the form of ready to drink beverages. For reasons of nutrition and/or for ease of formulation into drinks consumed (or likely to be consumed) by children and/or bought by parents to give to their children, presence in such RTD formulation of dairy components like casein micelles is preferred.
In particular, there is a desire for such RTD products which have a mouthfeel and/or texture in the mouth related to or similar to milk, as e.g. such RTD-products can be aimed at children (e.g. schoolchildren aged 6-12) and a product which (at least in mouthfeel and or texture) mimics (to some extent) milk (that is: more like milk than like e.g. a fruit juice or soft drink) is generally accepted by such children and/or their parents as being a nutritious product. Whilst colour and flavour can be made up by colourants and/or flavouring agents (and such is quite common for milk-like health drinks aimed at children, like flavouring with chocolate, banana or strawberry), the mouthfeel of milk or milk-like drinks is a bit more difficult to approach. It also requires that the formation of a sediment is preferably minimised, more preferably avoided. Even though a flavouring may be added, the presence of a cooked off-flavour is preferably avoided.
In addition to the milk-like mouthfeel or texture in the mouth, it is also desired that the RTD is packaged and heat-preserved (e.g. by heat-pasteurisation or heat-sterilisation). In addition to that, it is desired that the product shows minimal sedimentation upon production, and preferably shows no sedimentation at all upon production.
DE 4130284 discloses a process for the preparation of proteins having a high nutritional value. The process discloses hydrolysing whey containing alpha-lactalbumin high in tryptophan and cystein by pepsin, and the resulting product is blended with proteins, such as e.g. casein.